1. Field of the Invention
This invention relates to an oscillation circuit, an electronic circuit using that oscillation circuit, and a semiconductor device, electronic equipment, and timepiece using that oscillation circuit or electronic circuit.
2. Description of the Related Art
Oscillation circuits that use crystal oscillators are widely employed in the art in devices such as portable timepieces, portable telephones, and computer terminals. It is necessary to design such portable items of electronic equipment in such a manner that they are economical in their power consumption and have longer battery lives.
This crystal oscillation circuit comprises an inverting amplifier and a feedback circuit that is provided with a crystal oscillator. The inverting amplifier comprises a pair of transistors where the gate of each of these transistors is used as an input side and the drain thereof is used as an output side, by way of example. In this case, the drain sides of these two transistors are connected together and the source sides thereof are connected to ground and a power voltage side, respectively.
If the power voltage is applied to the inverting amplifier in the crystal oscillation circuit of this configuration, the phase of the output of the inverting amplifier is inverted through 180 degrees and the thus inverted signal is fed back to the gate of each transistor as an input. The transistors configuring the inverting amplifier are turned on and off alternately by the operation of this feedback, the oscillation output of the crystal oscillation circuit gradually increases, and thus the oscillator starts to oscillate stably.
However, the absolute value of a voltage Vreg applied to the inverting amplifier in this prior-art crystal oscillation circuit is set to be greater than the total of the absolute values of the threshold voltages VTP and VTN of the transistors in this circuit, as follows:|Vreg|>|VTP|+|VTN|  (1) 
The current inventors have discovered that this is the cause of a short-circuiting current IS that flows from the high potential side of the low potential side within the inverting amplifier, which causes a problem when trying to reduce the power consumption of the entire circuit.